Numerous methods and systems have been developed for conducting chemical, biochemical, and/or biological assays. These methods and systems are essential in a variety of applications including medical diagnostics, food and beverage testing, environmental monitoring, manufacturing quality control, drug discovery, and basic scientific research.
Depending on the application, it is desirable that assay methods and systems have one or more of the following characteristics: i) high throughput, ii) high sensitivity, in) large dynamic range, iv) high precision and/or accuracy, v) low cost, vi) low consumption of reagents, vii) compatibility with existing instrumentation for sample handling and processing, viii) short time to result, ix) multiplexing capability, and x) insensitivity to interferents and complex sample matrices. It is also desirable in many applications that these types of performance benefits are achieved with assay formats that are easy to carry out, are amenable to automation, and/or use stable dry reagents. There is substantial value to new assay methods and systems with these characteristics.
A variety of approaches have been developed that provide reagents for assays in dry stable form. U.S. Pat. No. 5,413,732 describes certain dry reagent spheres that are capable of dissolving in a solution.
U.S. Pat. No. 6,429,026 describes certain immunoassays using dry reagents and time-resolved fluorescence detection. A catching antibody is immobilized on the surface of a microtitration well. An insulating layer containing carbohydrate and/or protein is dried on top of the catching antibody at the bottom of the well. A labeled antibody is added in a small volume and dried on top of the insulating layer. The antibody is labeled with a lanthanide chelate that can be detected using dissociation enhance lanthanide fluoroimmunoassay (DELFIA) techniques. To start the immunoassay, a sample and a common assay buffer is added. After allowing the antibody reactions to occur, the well is washed several times, a DELFIA enhancement buffer is added, and a fluorescence lifetime measurement is carried out.
U.S. Publication 2003/0108973 describes a sandwich immunoassay that employed a test tube containing a lyophilized mixture comprising a capture antibody immobilized on 2.8 μm magnetizable polystyrene beads and a detection antibody labeled with an electrochemiluminescent label. The mixture could also include blocking agents to reduce non-specific binding of the detection antibody to the beads during the lyophilization process. Addition of sample containing the analyte of interest resulted in the formation of sandwich complexes on the beads. A suspension of beads was then aspirated into a reusable flow cell where they were collected on an electrode and analyzed using electrochemiluminescence (ECL) detection techniques.
U.S. Pat. No. 6,673,533 of Wohlstadter et al. describes an ECL-based sandwich immunoassay using dry reagents. A capture antibody was immobilized on a composite electrode. The other reagents used in assay were dried on the electrode surface by adding and lyophilizing a solution containing a detection antibody linked to an ECL label, phosphate, tripropylamine, bovine serum albumin, sucrose, chloracetamide, and TRITON X-100. Immunoassays were conducted by adding a sample to the dried reagents on the electrodes, incubating the solutions, and applying a potential to the electrode to induce ECL. No washing step was required.
A variety of techniques have been developed for increasing assay throughput. The use of multi-well assay plates (also known as microtiter plates or microplates) allows for the parallel processing and analysis of multiple samples distributed in multiple wells of a plate. Multi-well assay plates can take a variety of forms, sizes, and shapes. For convenience, some standards have appeared for instrumentation used to process samples for high-throughput assays. Multi-well assay plates typically are made in standard sizes and shapes, and have standard arrangements of wells. Arrangements of wells include those found in 96-well plates (12×8 array of wells), 384-well plates (24×16 array of wells), and 1536-well plates (48×32 array of wells). The Society for Biomolecular Screening has published recommended microplate specifications for a variety of plate formats (see http://www.sbsonline.org).
U.S. Publications 2004/0022677 and 2005/0052646 of U.S. application Ser. Nos. 10/185,274 and 10/185,363, respectively, of Wohlstadter et al. describe solutions that are useful for carrying out singleplex and multiplex ECL assays in a multi-well plate format. They include plates that comprise a plate top with through-holes that form the walls of the wells and a plate bottom sealed against the plate top to form the bottom of the wells. The plate bottom has patterned conductive layers that provide the wells with electrode surfaces that act as both solid-phase supports for binding reactions as well as electrodes for inducing ECL. The conductive layers may also include electrical contacts for applying electrical energy to the electrode surfaces.
Despite such known methods and systems for conducting assays, improved assay modules for conducting chemical, biochemical, and/or biological assays are needed.